Helium purification method and apparatus

ABSTRACT

Method and apparatus for removing condensable gaseous impurities from helium gas. The impure helium is cooled by indirect heat exchange with cold pure helium to condense out impurities. The fluid flow within the purifying heat exchanger is automatically controlled and cooling of the impure stream is periodic, being carried out during those periods when the heat exchanger registers a temperature within a predetermined range in its coldest section. Warm pure helium is used for periodic warmup to remove condensed impurities. The purification system is conveniently integrated into a cryostat such as that described in U.S. Pat. No. 2,458,894 or U.S. Pat. No. 3,250,079.

United States Patent Collins Feb. 19, 19741 [54] HELIUM PURIFICATION METHOD AND 3,060,697 10/1962 Collins 62/13 APPARATUS 3,490,245 1/1970 Muenger 1. 61/13 3,606,761 9/1971 Muenger 62/12 [75] Inventor: Samuel C. Collins, Belmont, Mass. A C T h l I FOREIGN PATENTS OR APPLICATIONS ssigneez I ryogenic ec no ogy, nc.,

waltham, Mass. 1,025,385 4/1966 Great Britain 62/12 [22] Filed: Mar. 24, 1970 Primary Examiner-Norman Yudkoff [21] APP] 22,262 Assistant ExaminerArthur F. lPurcell I Attorney, Agent, or FirmBessie A. Lepper 52 10.5. C1 62 40 62 12, 62 22, l 1 l 64/37 [57] ABSTRACT [51] Int. Cl. F25j 1/00, F25j 3/00 Method and apparatus for removing condensable gas- [58] Field of Search..... 62/9, 1 1, 22, 18, 40, I2, 37; eous impurities from helium gas. The impure helium is 55/62 cooled by indirect heat exchange with cold pure helium to condense out impurities. The fluid flow within [56] References Cited the purifying heat exchanger is automatically con- NI E STATES PATENTS trolled and cooling of the impure stream is periodic, 2,895,303 7 1959 Streeter 62/9 being Carried 9 during those i the heat 2309903 10/1959 zimmermannw 62/4O exchanger registers a temperature within a predeter- 3,057,167 10/1962 Yendal] I I I I 62/18 mined range'in its coldest section. Warm pure helium 3,233,418 2/1966 Shaievitz 62/9 is used for p r i w mup to remove condensed im- 3,250,079 5/1966 Davis 62/40 purities. The purification system is conveniently inte- 3,299,646 1/1967 Stuart". 62/9 grated into a cryostat such as that described in US. 3,340,699 9/1967 Post i 633/13 Pat. No. 2,458,894 or US. Pat. No. 3,250,079. 3,205,639 9/1965 Johnson. 55/62 2,715,820 8/1955 Becker 62/12 11 Claims, 4 Drawing Figures 121 b He /E RECOVERY ases: S n9 IMPURE He ,Pl

|35-TH|RD RESERVOIR 116 me .13 n5 PURIFYING HEAT iifiiig 154 i Ila-CHANGER Io\ SWITCH FIRST SOURCE 16....

l I 20 151 @{I :1 j 95 /52 53 24 .39 r: L 1 as-ra I37 '1 ELEMENT 65 i 11 6Q l5O't \L j Z i. i i :ii 11/101 2" I L11. If. A. I L, i

PATENIED FEB] 91924 SHEET 3 UF 4 KS n O M 16 s m4 U L O S Y B 2 mmnm Attorney PATENT En FEB 1 9 1914 saw u 0F 4 mmDm INVENTOR. Samuel C. Collins HELIUM PURIFICATION METHOD AND APPARATUS This invention relates to a method and apparatus for removing impurities from helium gas and more particularly to method and apparatus which operate automatically in conjunction with a helium refrigerator/liquefier or a source of liquid helium. The invention is also applicable to the purification of the more easily condensable gases.

In the use of gaseous helium to develop refrigeration at cryogenic temperatures, whether or not the helium is liquified, it is necessary to pass the gaseous helium through several heat exchange systems of increasingly lower temperatures which may be as low as a few tenths ofa degree Kelvin. This in turn requires that the helium gas be as completely free of any gaseous contaminants as it is possible to make it. The presence of any contaminants would very rapidly plug the heat exchange passages by freezing out as solids at these low temperatures making the cryogenic apparatus inoperative. In circulation through even a closed system, the helium gas picks up these gaseous contaminents which may include carbon dioxide, air (and hence oxygen, nitrogen and argon) hydrogen and water vapor. When the helium is withdrawn from the cryostat and used to cool external loads the amountof these impurities picked up by it may be materially increased.

Such gaseous impurities are commonly removed by passing the gas to be purified through one or more cold beds of charcoal or by freezing out in a heat exchanger. When the charcoal of a charcoal trap is fresh, gaseous impurities are absorbed with relatively high efficiency, but to rely entirely on such charcoal traps would result in having to regenerate them very often. Moreover there is no simple, inexpensive way of checking the pu rified helium for impurity content. In U.S. Pat. No. 2,895,303 apparatus was disclosed which achieved helium cleanup by freezing out the impurities in a heat exchange system. Although this apparatus provides a reli able and efficient means for removing gas impurities it has been found that the need for introducing an externally supplied warm gas into the heat exchanger to vaporize the condensed impurities requires a considerable amount of time. Moreover, the apparatus of U.S. Pat. No. 2,895,303 requires an operator to observe the temperature of a helium gas thermometer to check the purity of the purified gas discharged to determine when the impure helium supply must be cutoff and the condensed contaminants vaporized for removal. The present invention provides method and apparatus for purifying helium gas which is self-controlling, which requires no externally supplied warming gas and which is completely automatic.

It is therefore a primary object of this invention to provide improved apparatus for use in connection with a cryogenic apparatus or a source of liquid helium for purifying gaseous helium. It is another object of this invention to provide apparatus of the character described which is completely automatic in all its operational aspects and which is capable of purifying a greater quantity of helium over a given period of time than heretofore attainable. Still another object is to provide such apparatus which requires no externally supplied warming gas and which removes the impurities as liquids rather than gases. It is another primary object of this invention to provide a continous, automatically controlled method of purifying helium gas. Other objects of the invention will in part be obvious and will in part be apparent hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified. in the following detailed disclosure and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the follow ing detailed description taken in connection with the accompanying drawings in which FIG. I is a diagrammatic representation of the purifying system of this invention as it is connected into a helium refrigerator/liquefier;

FIG. 2 illustrates the fluid flow in the system during cool down;

FIG. 3 illustrates the fluid flow in the system during purification; and

FIG. 4 illustrates the fluid flow in the system during regeneration and impurity dumping.

In brief, the apparatus of this invention comprises a counterflow purifying heat exchanger in which a stream of impure helium is directed through a first channel to be cooled progressively from room temperature to that temperature at which the most volatile of the impurities has a negligible vapor pressure. For nitrogen this of the order of 30K and for hydrogen about 6K. The cooling is accomplished by sending a stream of cold pure helium which is derived from an operating helium liquefier or refrigerator (such as described in U.S. Pat. No. 2,458,894 or U.S. Pat. No. 3,250,079) or from a vessel containing stored liquid helium through a second channel of the purifying heat exchanger. This stream of pure helium is greatly augmented by adding to it the purified residue of the original impure stream. Fluid flow of the two streams through the purifying heat exchanger is controlled automatically by a series of pressure switches (which in turn are governed by temperatures and pressures at certain flow points) and trap means are provided to collect liquid impurities which are periodically discharged from the purifying heat exchanger.

The purification system of this invention is shown in the drawings to be connected to a cryostat such as that described in U.S. Pat. No. 2,458,894 or U.S. Pat. No. 3,250,079. The main heat exchanger system of this cryostat is generally indicated by the reference numeral 10 and the heat exchanger system of the purifying system by the numeral 11. These heat. exchanger systems along with certain of their associated components are contained within an insulated, normally evacuated housing 13 designated in the drawings by the dot-dash line.

The main cyrostat heat exchanger 15 is of the type which permits high-pressure warm incoming helium gas to flow in one passage 16 in a direction countercurrent to the flow of low-pressure cold return helium in passage 17 in indirect heat exchange with the hightice the high-pressure helium after partial cooling is diverted through a cold charcoal trap 18 by way of a conduit 19 and after passage through the trap it is split into two streams, one of which is returned by a conduit 20 to the high-pressure side of the heat exchanger, the other of which is taken by conduit 21 into an expansion engine 22 where it is cooled by expansion. From the expansion engine 22 the cold helium at a reduced pressure is discharged into conduit 23 which is in fluid communication with the lowpressure passage 17 of the heat exchanger as well as with conduit 24 which serves as a first fluid connection with the purifying heat exchange system 11.

After further cooling the high-pressure helium is again diverted by conduit 25 into a second colder charcoal trap 26 from which a portion is returned via conduit 28 to the high-pressure side of the heat exchanger and the remainder is introduced via line 29 into a second expansion engine 30, the expanded further cooled gas from which is returned to the low-pressure side of the heat exchanger 15. Fluid conduits 32 and 33 provide fluid communication between the high-pressure side of the cryostat heat exchanger and the purifying heat exchange system 11. Conduit 33 joins conduit 24 to form a single conduit 34.

The Joule-Thomson heat exchanger 40 follows heat exchanger 15 and the high-pressure line 16 is shown to terminate in a Joule-Thomson expansion valve 41. Liquefied helium may be withdrawn from the liquid reservoir (not shown) through line 42, the fluid flow in which is controlled by valve 43. FIG. 1 illustrates a lowpressure helium return line 44, the fluid flow through which is controlled by valve 45. This arrangement is similar to that in US. Pat. No. 3,250,079 wherein liquefied helium or cold helium gas may be circulated to a load and returned to the cryostat. Alternatively, Joule-Thomson heat exchanger and valve 41 may be eliminated in the cryostat and conduit 42 may be connected directly to the high-pressure side of heat exchanger 15. In this case, the conduits 42 and 44 may take the form of the remote delivery tube which serves as the Joule-Thomson heat exchanger as in US. Pat. No. 3,201,947, and the Joule-Thomson expansion valve may then be placed at the end of the delivery tube to permit liquefaction to be accomplished directly in a storage vessel.

The purifying heat exchanger system 11 comprises a heat exchanger 50 constructed to provide two fluid flow passages 51 and 52 adapted to effect indirect heat exchange between fluids flowing therethrough. The first of these passages 51 is in fluid communication with conduit 34, noted previously to be in communication with both the low-pressure side 17 of the cryostat heat exchanger 15 through conduit 24 (the fluid flow in which is controlled by valve 53) and with the highpressure side 16 of heat exchanger 15 through conduit 33 (the fluid flow in which is controlled by valve 54). The second passage 52 of heat exchanger 50 is connected through conduit 32 (the fluid flow in which is controlled by valve 55) to the high'pressure side of the cryostat heat exchanger 15. The fluids flowing in conduits 32 and 34 pass through a purifier filter 60 which has a temperature-sensitive element 61, such as a hydrogen vapor pressure bulb connected to an indicator 62 such as a calibrated pressure gage for monitoring the temperature of fluid flowing in conduits 32 and 34.

Valves 53, 54 and 55 are located within the insulated housing 13 and are mechanically actuated. They are of the extended-stem type, the stem 65 of valve 53 terminating in a gas-driven piston means 66; the stem 67 of valve 54 terminating in a similar gas-driven piston means 68; and the stem 69 of valve 55 terminating in a similar gas driven piston means 70. A gas-equalizing line 71 connects the piston means 68 and 70. The flow of pressurized gas for the pneumatic actucation of the piston means, and hence for the actuations of valves 53, 54 and 55, is controlled by solenoid switch valve 75 which is continually supplied with high'pressure fluid through branch conduit 76 connected to the main highpressure line 77 of the cryostat. High-pressure branch conduit 76 has associated with it an automatic pressure-controlling valve 78 which continuously limits the pressure of the fluid delivered to valve 75. (Typically this pressure is limited to about 150 p.s.i.). The branched fluid line 80 connects valve 75 with the piston means 66, 68 and 70 to deliver gas to or withdraw gas from the pistons. Valve 75 is also connected by conduit 81 to the main low-pressure line 82 of the cryostat. One or more compressors 83 join the low-pressure ant .-i hzare talip 82 ns --77..9 the qxq ta Positioned within purmirig heat exchanger 50 in the coldest area is a hydrogen vapor pressure bulb 85. Connected to this vapor pressure bulb are pressure switch 86, pressure switch 87 and a temperature indicator 88. Pressure switch 86 is adapted to operate as a function of temperature. Pressure switch 87 is a dual pressure switch connected to bulb and is adapted to operate as a function of temperature. In its first operational mode it is normally open and set to close on decreasing temperature at a first preset temperature, e.g., 29K; while in its second operational mode it is closed at the first preset temperature and opens on increasing temperature at a second preset temperature, e.g., 31K.

Two impurity discharge lines 93 and 94 are provided to periodically dump the impurities as liquids or gases from traps 95 and 96. Line 93 removes liquid air while line 94 removes liquid water and CO during warmup of the cycle. The liquid flow in lines 93 and 94 is controlled by solenoid valves 97 and 98, respectively. Valves 99 and 100 are provided as relief valves. Valves 97 and 98 are actuated, respectively, by a combination of pressure switch 86 and time delay switch 101 and by a combination of pressure switch 146 and time delay switch 101 as will be explained in detail below. it will also be seen that pressure switch 86 actuates valve 75. (In the drawings, dotted lines are used to indicate connections between the various switches and the valves with which they are connected).

As will become apparent from the description of the cycle operation (to be presented below) the directions of flow of fluids in the passage 51 and 52 of the purify ing heat exchanger 50 are automatically reversed, and the fluids must be directed in one of two alternative flow paths depending upon their direction of flow. in the case of the pure helium flowing within passage 51 of the purifier heat exchanger 50 the fluid is directed either into the low-pressure side of the cryostat or withdrawn from the high-pressure side. Conduit 105, which is connected to the pure helium passage 51, therefore branches into line 106 which is in fluid communication with the low-pressure side and line 107 which is in fluid communication with the high-pressure side of the cryostat. Line 108 provides a fluid connection between line 106 and high-pressure line 77 of the cryostat. Between the point of branching and joining with passage 51 of heat exchanger 50, conduit 105 is in indirect heat exchange relationship with a heater 110 which is controlled by a temperature switch 111 adapted to sense the temperature of the fluid flowing in conduit 105.

FIG. 1 illustrates the means by which the flow of fluid is controlled within the cryostat itself. Although a part of this flow control means is not directly connected into the purifying apparatus of this invention it is shown in outline to complete the description of the apparatus. Thus the solenoid valve 115, the pressure indicator 116, the flow control valves 117 and 118, the helium recovery tank 119, the conduit 120 communicating between the tank and the pure helium supply and the flow control valve 121 are not integral parts of the purifying system but are components of the cryostat system into which the purifying apparatus itself is integrated. These components are directed to the automatic control of pure makeup helium which must be introduced in the cryostat to supply an amount of helium equivalent to that removed as liquid helium or lost in other ways.

It will be seen that branch conduit 106 is connected to a conduit 125 which joins the pure helium makeup line 120 and the main low-pressure line 82 of the cryostat. In conduit 125 is a solenoid valve 126 which controls the flow of makeup helium to the cryostat from the pure helium gas supply (not shown). This is a hand start valve. Also in line 125 are valves 127 and 128. Valve 127 is an automaticallyoperating gas regulator valve which determines the pressure of the fluid in the low-pressure line; and valve 128 is a protection valve for valve 127. An automatic fluid regulator valve 129 is located in line 108 to supply any desired extra gas to the make-up regulator valve 127; while restriction valve 130 and check valve 131 in line 106 control the maximum fluid flow in this line.

The flow of fluid in branch conduit 107, which joins passage 51 of the purifying heat exchanger with the high-pressure line of the cryostat, is controlled by solenoid valve 133 which in turn is closed by pressure switch 86. An automatically controlled valve 134 is also located in conduit 107, the purpose of this valve being to regulate the flow of heating helium entering the pure helium side of the heat exchanger through valve 133 when it is open.

The impure helium to be purified is delivered into a gas bag 135 from which it is taken by line 136 through a compressor 137 and stored in cylinders 138. Communication between the impure helium storage cylinders 138 and the impure helium passage 52 of the purifying heat exchanger 50 is by way of conduit 139 which joins the main impure helium flow line 140. Associated with this main impure helium line are a pressure indicator 145, a pressure switch 146, a solenoid actuated valve 147 and a pressure relief valve 148. Associated with conduit 139 are an automatic fluid regulating valve 150, a manually operated valve 151 and a solenoid valve 152 which is actuated by pressure switches 86, 87 and 146. Conduit 139 also has a relief line 153 and re lief valve 154 branching off from it.

With the completion of the identification of all the valves and pressure switches his now possible to indicate the remaining connections between them before giving a full description of an operation cycle of the purifying cycle. It will be seen that solenoid valves 75 and 133 are actuated by pressure switches 86 and 146; solenoid valves 152 by pressure switches 86, 87 and 146; solenoid valve 97 by pressure switch 86 and time delay 101; and solenoid valves 98 and 147 by pressure switch 146 and time delay 101. I

In the following description of a typical operational cycle certain operational parameters are used as exemplary. lt will, of course, be appreciated that these parameters as given herein as being illustrative only may be varied, and it is therefore not meant to limit the scope of either the apparatus or method apparatus of this invention to these operational parameters.

The hydrogen pressure bulb is exposed to the coldest section of the purifying heat exchanger and the change in the pressure of the hydrogen within the bulb with the temperature to which the bulb is exposed is used as one of the primary means of valve actuation and hence of fluid flow control. As noted previously, pressure switches 86 and 87 are connected to this vapor pressure bulb. Pressure switch 86 is set to be opened on rising temperatures at approximately 80K to energize and close solenoid-actuated valves 53, 133, and 97, and to open solenoid-actuated valves 54 and 55. Pressure switch 87 is a dual-pressure switch and in its first mode of operation it is set to close at approximately 29K in the example used here, and in its second mode of operation to open at about 31K to control solenoid valve 152. Finally, pressure switch 146 which senses the pressure in the main impure helium flow line is set to energize the solenoids associated with valves 98, 147 and 152 to open valves 98 and 147 and to close valve 152 when the pressure in line 140 reaches 350 psi. which indicates the buildup of condensed impurities in the heat exchanger and the need for impurity dumping. Valve 98 is closed by time delay switch 101 in approximately 60 seconds after opening; and at the same time valve 97 is also opened by time delay 101. The role of valve 75 is to mechanically open and close valves 53, 54 and 55 through their associated pneumatically operated piston drives 66, 68 and 70. High-pressure helium from the main high-pressure line of the cryostat is continuously delivered through line 76 at a pressure of about psi. (controlled by valve 78) to valve 75 which is normally vented to low pressure valve line 82. In this normal condition, valves 54 and 55 are closed and valve 53 is open. The operation of valve 75 is controlled in turn by pressure switches 86 and 146, switch 146 serving to actuate valve 75 to keep it in its normal vented condition which keeps valves 54 and 55 closed and 53 open, and switch 86 serving to permit high-pressure gas to enter valve 75 to open valves 54 and 55 and close valve 53.

In defining the apparatus and in describing the cycle of this invention it will be convenient to refer to the conduit means as first, second, etc.., and therefore the following tabulation is presented to identify these conduit means in terms of the reference numerals in the drawings, as well as the valves and pressure switches which control the flow in the conduit means.

Drawing Switch Numbers Conduit means first second third fourth fifth sixth seventh eighth The following description of the operation of the apparatus and method of this invention is given in terms of supplying cold high-pressure helium gas from a cryostat. It will, of course, be apparent to those skilled in the art that this cold helium gas may be supplied from a source of liquid helium from which the cold gas is vaporized.

The purification cycle is begun by manually closing valve 126 which controls the flow of makeup pure helium into the cryostat when liquefaction of helium is being accomplished. Cutting off the flow of pure helium gas from the pure helium storage forces a portion of the cold helium to flow from the high-pressure side of the cryostat along the first conduit means through the pure helium side 51 of the purifying heat exchanger 50. Thus cooldown of the purifying heat exchanger is accomplished and the flow of pure cold high-pressure helium is as illustrated by the heavy line in FIG. 2. This means that valve 54 is open and valve 127 functions to regulate the pressure in the low-pressure line 82 of the cryostat. As the pure helium leaves the purifying heat exchanger it is taken via th fourth conduit means to the low-pressure line 82 of the cryostat. Valve 55 opens to flush the purifier filter 60 and to pressurize the passage 51 of the purifying heat exchanger with pure helium. Valve 53 is closed as are those valves which control the flow of impure helium into the purifying heat exchanger. Heater 110 is turned on.

In this illustrative cycle example, when the cold end of the purifying heat exchanger reaches 29K, purifying begins. At this temperature pressure switch 87 energizes the solenoid associated with valve 152 to open it to allow impure helium to flow through conduit 139 into main impure helium line 140 (i.e. via the sixth conduit means) andthrough the purifying heat exchanger 50 in passage 52. The fluid flow during purification is shown in FIG. 3 by the heavy lines. As the impure helium in passage 52 becomes colder and colder the impurities are condensed out as liquids which then solidify, and the helium leaving the purifying heat exchanger through conduit 52 (third conduit means) is sufficiently pure to be introduced into the high-pressure side 16 of the main cryostat heat exchanger at essentiably the same temperature level at which the cold pure helium continues to be withdrawn from passage through the purifying heat exchanger.

As the impure helium continues to flow through the purifying heat exchanger its thermal load is such that the heat exchanger begins to warm up. In this cycle example, when the temperature of the heat exchanger reaches 31K, as determined by the hydrogen vapor bulb, pressure switch 87 opens which in turn effects the closing of valve 152 to close off the flow of impure helium through the purifying heat exchanger. The fluid flow is again that shown in FIG. 2 and cooldown begins again by virtue of the fact that cold pure helium continues to flow through the purifying heat exchanger 50. As soon as the temperature has dropped again to 29K, pressure switch 87 opens valve 152 and purification is continued. Thus in this example since the purification heat exchanger can never accept impure helium when it is above 31K, the supply of impure helium is automatically turned on and off, the fluid flow alternating between the flow patterns of FIGS. 2 and 3. The heater 110 remains on throughout these steps.

During purification periods the deposit of impurities in the purifying heat exchanger is continued. The buildup of solid impurities is marked by an increase in pressure drop across the purifying heat exchange. This pressure is sensed by pressure switch 146. When gas pressure in main impure helium line 140 reaches 350 psi. (or some other preset pressure), pressure switch 146 closes valve 152, deenergizes valve (which in turn effects the closing of valves 54 and 55 and the opening of valve 53) and opens valves 133, 147 and 98. Valves 147 and 98 are automatically closed after 60 seconds by the time delay mechanism 101. The fluid flow pattern during this period of warmup regeneration is that which is shown in heavy continuous lines in FIG. 4. It will be seen that the directions of fluid flow are reversed, that is warm high-pressure pure helium sweeps along the fifth conduit means, through the pure helium side of the purifying heat exchanger and into the lowpressure side of the cryostat heat exchanger via conduits 34 and 24 (second conduit means) and valve 53. The warmed residual impure helium in the purifying heat exchanger is swept out into the gas bag 135 as lowpressure gas through conduit 140 (seventh conduit means); and simultaneously the impurities which were liquefied and collected in trap 95 (liquid air) and trap 96 (water), are dumped. Valves 97 and 98 are those which control fluid flow in conduits 93 and 94 (eighth and ninth conduit means) through which these impurities are dumped. Valve 97 is opened by time delay switch 101 and closed by pressure switch 86 at about K; and valve 98 is opened by pressure switch 146 and closed by time delay switch 101. Pressure switch 86 is set to close vlaves S3, 97 and 133 when the temperature in the purifying heat exchanger reaches 80K in this cycle example and to open valves 54 and 55 by energizing valve 75. The flow of impurities from traps and 96 is illustrated by the heavy dashed lines in FIG. 4. It will be noted that at the completion of this step, as illustrated in FIG. 4, the cycle is in condition to begin again with the cooldown step of FIG. 2.

If a source ofliquid helium, e.g., a dewar storage vessel containing liquid helium under pressure, is to be substituted for the cryostat, then conduits 32 and 33 will communicate with the interior of the storage vessel and conduit 24 will communicate directly with a lowpressure pure helium line.

The method and apparatus of this invention are, of course, applicable to the purification of the higher boiling gases, e.g., hydrogen, deuterium, and neon. The description has been presented in terms of purifying helium, the lowest boiling gas, since it places the most stringent requirements on such a purification device.

It will be seen from the above description of the apparatus of this invention and of the cycle on which it operates that there is provided a completely automatic, reliable and highly efficient system for removing impurities from helium so that the resulting purified helium may be used in cryogenic apparatus. Such a system may be integrated with a cryostat and offers an economical way of recovering valuable helium gas.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the construction set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. An apparatus for purifying gaseous helium, comprising in combination a. a first source of pure, cold, high-pressure helium;

b. a first reservoir of pure, cold, low-pressure helium;

c. a second source of pure, essentially roomtemperature, high-pressure helium;

d. a second reservoir of pure, essentially roomtemperature, low-pressure helium;

e. a third source of high-pressure impure helium;

f. a third reservoir of low-pressure impure helium;

g. a purifying heat exchanger having a first pure helium flow passage and a second helium flow passage, said passages being arranged to effect indirect heat exchange between the helium streams flowing therein;

h. first fluid conduit means to conduct said pure,

cold, high-pressure helium through said first passage from said first source to said second reservoir and second fluid conduit means to conduct said high-pressureimpure helium through said second passage from said third source to said first source during such periods when the lowest temperature within said heat exchanger ranges between preset levels and until a preset quantity of impurities has condensed in said second passage;

. third fluid conduit means to conduct high-pressure helium from said second source through said first passage to said first reservoir and fourth fluid conduit means to discharge warmed helium from said second passage to said third reservoir;

j. means to discharge the condensed fluid impurities from said heat exchanger;

k. temperature sensing means positioned within the coldest section of said purifying heat exchanger;

1. first and second pressure-actuated switch means adapted to operate as a function of temperature and connected in signal receiving relationship to said temperature sensing means;

m. third pressure-actuated switch means responsive to the pressure of said high-pressure impure helium flowing in said second fluid conduit means;

11. first valve means adapted to control fluid flow in said first and third fluid conduit means and actuable by said first and third pressure-actuated switch means;

0. second valve means adapted to control fluid flow in said second fluid conduit means and actuable by said second pressure-actuated switch means; and

p. third valve means adapted to control fluid flow in said fourth fluid conduit means and actuable by said third pressure-actuated switch means.

2.'An apparatus in accordance with claim 1 wherein said first source and said first reservoir are the highpressure and low-pressure fluid passages, respectively, of the main heat exchanger of a helium liquefier.

3. An apparatus in accordance with claim 1 wherein said second source and said second reservoir are the high-pressure and low-pressure fluid lines, respectively,

of a helium liquefier.

4. An apparatus for purifying gaseous helium, comprising in combination a. a source of pure, cold, high-pressure helium;

b. a-reservoir of pure, cold, low-pressure helium;

c. a source of pure, essentially room-temperature,

high-pressure helium;

d. a reservoir of pure, essentially room-temperature,

low-pressure helium;

e. a source of high-pressure impure helium;

f. a reservoir of low-pressure impure helium;

g. a purifying heat exchanger having a first pure helium flow passage and a second helium flow passage, said passages being arranged to effect indirect heat exchange between the helium streams flowing therein;

h. liquid impurity trap means within said purifying heat exchanger;

i. a vapor pressure bulb positioned within the coldest section of said purifying heat exchanger;

j. first and second pressure-actuated switch means in signal receiving relationship with said vapor pressure bulb;

k. first fluid conduit means connecting said source of pure, cold, high-pressure helium with the cold end of said first flow passage in said purifying heat exchanger;

. second fluid conduit means connecting said source of pure, cold, high-pressure helium with the cold end of said second flow passage in said purifying heat exchanger;

in. third fluid conduit means connecting said reservoir of pure, cold, low-pressure helium with the cold end of said first flow passage in said purifying heat exchanger;

n. fourth fluid conduit means connecting the warm end of said first fluid flow passage in said purifying heat exchanger with said source of pure, essentially room-temperature, high-pressure helium;

o. fifth fluid conduit means connecting the warm end of said first fluid flow passage in said purifying heat exchanger with said reservoir of pure, essentially room temperature, low-pressure helium;

p. sixth fluid conduit means connecting the warm end of said second fluid flow passage in said purifying heat exchanger with said source of high-pressure impure helium;

q. third pressure-actuated switch means associated with said sixth fluid conduit means;

r. seventh fluid conduit means connecting the warm end of said second fluid flow passage with said reservoir of low-pressure impure helium;

. eighth fluid conduit means in fluid communication with said liquid impurity trap means;

. time delay switch means;

purifying filter means associated with said first,

second and third conduit means;

v. valve means associated with each of said eight fluid conduits meansand adapted to control the flow of fluids within said conduits and through said purifying heat exchanger, said valve means being actuated by said pressure switches thereby to permit 1. helium to flow from said cold high-pressure pure helium source through saidpurifying heat exchanger to said reservoir of essentially roomtemperature, low-pressure, pure helium until the pressure in said sixth fluid conduit means reaches a first predetermined level indicative of the presence of a predetermined quantity of impurities in said second flow passage in said purifying heat exchanger,

2. helium to flow from said source of high-pressure impure helium through said purifying heat exchanger, wherein impurities are removed by condensation, to said source of pure, cold, highpressure helium during those periods of helium flow (1) when the heat exchanger temperature sensed by said vapor bulb is rising within a predetermined temperature range,

3. helium to flow from said source of pure essentially room temperature high-pressure helium through said purifying heat exchanger to said reservoir of pure cold low-pressure helium from the time when the pressure in said sixth fluid conduit means reaches said predetermined level until the temperature in said purifying heat exchanger reaches a preset level,

4. warmed impure helium to flow from said second passage in said purifying heat exchanger to said reservoir of low-pressure impure helium during helium flow (3),

5. impurities to be discharged from said trap means for a predetermined period of time controlled by said time delay switch means and said first switch means, and

6. helium to begin to flow again from said cold high-pressure, pure helium source to start the cycle as in (l).

5. An apparatus in accordance with claim 4 wherein said source of pure, cold, high-pressure helium is the high-pressure fluid passage of the main heat exchanger of a helium liquefier and said reservoir of pure, cold, low-pressure helium is the low-pressure fluid passage of said main heat exchanger.

6. An apparatus in accordance with claim 4 wherein said source of pure, essentially room-temperature, high-pressure helium is the high-pressure fluid line of a helium liquefier and said reservoir of pure, essentially room-temperature, low-pressure helium is the low pressure fluid line of a helium liquefier.

7. An apparatus in accordance with claim 6 wherein said valve means in said first, second and third fluid conduit means are operated by piston driving means pneumatically actuated by helium gas supplied from said high pressure line of said helium liquefier and discharged into said low-pressure line of said cryostat, and wherein the flow of helium into and discharged from said piston driving means is controlled by a solenoid valve actuated by said first and third pressure switch means.

8. An apparatus in accordance with claim 4 wherein said valve means in said first through said fifth fluid conduit means are actuated by said first and third pressure switch means, said valve means in said sixth fluid conduit means is actuated by said first, second and third pressure switch means, said valve means in said seventh fluid conduit means are actuated by said third pressure switch means and said time delay switch means, and said valve means in said eighth fluid conduit means are actuated by said first pressure switch means, said time delay switch means and said third pressure switch means.

9. A method of purifying helium, comprising the steps of a. refrigerating a second periodically flowing stream of high-pressure impure helium, containing impurities to be removed, by indirect heat exchange with a countercurrently continuously flowing first stream of cold high-pressure pure helium withdrawn from a first source and directed to a reservoir of pure low-pressure helium thereby to produce a stream of purified cold, high-pressure helium for delivery to said first source, said heat exchange between said first and second streams being confined to a single purifying heat exchanger and the periodic flow of said second stream being regulated so that said second impure helium flows in heat exchange with said first stream during those periods when the temperature of said second stream is increasing within a preset temperature range and ceases to flow during those periods when the temperature of said second stream is decreasing within said preset temperature range, whereby said impurities are condensed out in said second stream and accumulated;

b. continuing the heat exchange between said first and second streams as in step (a) until the pressure drop experienced by said second stream increases to a preset pressure level by virtue of the condensation of said impurities within said second stream;

c. cutting off the flow of said first and second streams while warming the residual helium in said second stream by indirect heat exchange with warm, pure high-pressure helium of a third stream flowing between a second source and a low-pressure, pure cold helium reservoir in a direction opposite to the direction of said first stream in step (a) thereby forcing said residual helium in said second stream to flow in a direction opposite to the direction of said second stream in step (a) to a low-pressure, impure helium reservoir and to vaporize or liquefy said impurities;

d, discharging said impurities for a set period of time;

; e. cutting off the flow of said impurities;

f, beginning the continuous flow of said first stream as in step (a); and

g. then beginning the periodic flow of said second stream as in step (a) when the temperature reaches the lower level of said preset temperature range.

10. A method in accordance with claim 9 wherein said preset temperature range in step (a) is between about 29K and about 31K.

11. A method in accordance with claim 9 wherein said preset pressure level in step (b) is about 350 psi. 

2. An apparatus in accordance with claim 1 wherein said first source and said first reservoir are the high-pressure and low-pressure fluid passages, respectively, of the main heat exchanger of a helium liquefier.
 2. helium to flow from said source of high-pressure impure helium through said purifying heat exchanger, wherein impurities are removed by condensation, to said source of pure, cold, high-pressure helium during those periods of helium flow (1) when the heat exchanger temperature sensed by said vapor bulb is rising within a predetermined temperature range,
 3. helium to flow from said source of pure essentially room temperature high-pressure helium through said purifying heat exchanger to said reservoir of pure cold low-pressure helium from the time when the pressure in said sixth fluid conduit means reaches said predetermined level until the temperature in said purifying heat exchanger reaches a preset level,
 3. An apparatus in accordance with claim 1 wherein said second source and said second reservoir are the high-pressure and low-pressure fluid lines, respectively, of a helium liquefier.
 4. warmed impure helium to flow from said second passage in said purifying heat exchanger to said reservoir of low-pressure impure helium during helium flow (3),
 4. An apparatus for purifying gaseous helium, comprising in combination a. a source of pure, cold, high-pressure helium; b. a reservoir of pure, cold, low-pressure helium; c. a source of pure, essentially room-temperature, high-pressure helium; d. a reservoir of pure, essentially room-temperature, low-pressure helium; e. a source of high-pressure impure helium; f. a reservoir of low-pressure impure helium; g. a purifying heat exchanger having a first pure helium flow passage and a second helium flow passage, said passages being arranged to effect indirect heat exchange between the helium streams flowing therein; h. liquid impurity trap means within said purifying heat exchanger; i. a vapor pressure bulb positioned within the coldest section of said purifying heat exchanger; j. first and second pressure-actuated switch means in signal receiving relationship with said vapor pressure bulb; k. first fluid conduit means connecting said source of pure, cold, high-pressure helium with the cold end of said first flow passage in said purifying heat exchanger; l. second fluid conduit means connecting said source of pure, cold, high-pressure helium with the cold end of said second flow passage in said purifying heat exchanger; m. third fluid conduit means connecting said reservoir of pure, cold, low-pressure helium with the cold end of said first flow passage in said purifying heat exchanger; n. fourth fluid conduit means connecting the warm end of said first fluid flow passage in said purifying heat exchanger with said source of pure, essentially room-temperature, high-pressure helium; o. fifth fluid conduit means connecting the warm end of said first fluid flow passage in said purifying heat exchanger with said reservoir of pure, essentially room temperature, low-pressure helium; p. sixth fluid conduit means connecting the warm end of said second fluid flow passage in said purifying heat exchanger with said source of high-pressure impure helium; q. third pressure-actuated switch means associated with said sixth fluid conduit means; r. seventh fluid conduit means connecting the warm end of said second fluid flow passage with said reservoir of low-pressure impure helium; s. eighth fluid conduit means in fluid communication with said liquid impurity trap means; t. time delay switch means; u. purifying filter means associated with said first, second and third conduit means; v. valve means associated with each of said eight fluid conduit means and adapted to control the flow of fluids within said conduits and through said purifying heat exchanger, said valve means being actuated by said pressure switches thereby to permit
 5. An apparatus in accordance with claim 4 wherein said source of pure, cold, high-pressure helium is the high-pressure fluid passage of the main heat exchanger of a helium liquefier and said reservoir of pure, cold, low-pressure helium is the low-pressure fluid passage of said main heat exchanger.
 5. impurities to be discharged from said trap means for a predetermined period of time controlled by said time delay switch means and said first switch means, and
 6. An apparatus in accordance with claim 4 wherein said source of pure, essentially room-temperature, high-pressure helium is the high-pressure fluid line of a helium liquefier and said reservoir of pure, essentially room-temperature, low-pressure helium is the low-pressure fluid line of a helium liquefier.
 6. helium to begin to flow again from said cold high-pressure, pure helium source to start the cycle as in (1).
 7. An apparatus in accordance with claim 6 wherein said valve means in said first, second and third fluid conduit means are operated by piston driving means pneumatically actuated by helium gas supplied from said high pressure line of said helium liquefier and discharged into said low-pressure line of said cryostat, and wherein the flow of helium into and discharged from said piston driving means is controlled by a solenoid valve actuated by said first and third pressure switch means.
 8. An apparatus in accordance with claim 4 wherein said valve means in said first through said fifth fluid conduit means are actuated by said first and third pressure switch means, said valve means in said sixth fluid conduit means is actuated by said first, second and third pressure switch means, said valve means in said seventh fluid conduit means are actuated by said third pressure switch means and said time delay switch means, and said valve means in said eighth fluid conduit means are actuated by said first pressure switch means, said time delay switch means and said third pressure switch means.
 9. A method of purifying helium, comprising the steps of a. refrigerating a second periodically flowing stream of high-pressure impure helium, containing impurities to be removed, by indirect heat exchange with a countercurrently continuously flowing first stream of cold high-pressure pure helium withdrawn from a first source and directed to a reservoir of pure low-pressure helium thereby to produce a stream of purified cold, high-pressure helium for delivery to said first source, said heat exchange between said first and second streams being confined to a single purifying heat exchanger and the periodic flow of said second stream being regulated so that said second impure helium flows in heat exchange with said first stream during those periods when the temperature of said second stream is increasing within a preset temperature range and ceases to flow during those periods when the temperature of said second stream is decreasing within said preset temperature range, whereby said impurities are condensed out in said second stream and acCumulated; b. continuing the heat exchange between said first and second streams as in step (a) until the pressure drop experienced by said second stream increases to a preset pressure level by virtue of the condensation of said impurities within said second stream; c. cutting off the flow of said first and second streams while warming the residual helium in said second stream by indirect heat exchange with warm, pure high-pressure helium of a third stream flowing between a second source and a low-pressure, pure cold helium reservoir in a direction opposite to the direction of said first stream in step (a) thereby forcing said residual helium in said second stream to flow in a direction opposite to the direction of said second stream in step (a) to a low-pressure, impure helium reservoir and to vaporize or liquefy said impurities; d. discharging said impurities for a set period of time; ; e. cutting off the flow of said impurities; f. beginning the continuous flow of said first stream as in step (a); and g. then beginning the periodic flow of said second stream as in step (a) when the temperature reaches the lower level of said preset temperature range.
 10. A method in accordance with claim 9 wherein said preset temperature range in step (a) is between about 29*K and about 31*K.
 11. A method in accordance with claim 9 wherein said preset pressure level in step (b) is about 350 psi. 